For the longest time, Microsoft has been seen as an enemy of all things open, with former CEO Steve Ballmer famously describing Linux as a "cancer" in a 2001 interview with the Chicago Sun-Times. But attitudes and opinions have shifted in the intervening years. As Russinovich told the audience, almost all companies these days depend on at least some open source software, and that includes Microsoft customers. This has forced the company to warm to, and support, open source software—witness the proclamation by CEO Satya Nadella last October that "Microsoft loves Linux."

Supporting open source software is valuable, but more profound, and more important, is the adoption of open source ideals. Developers, in particular, have come to expect openness in development. This influence has seen Microsoft do things that once might have been considered unthinkable; after early pioneering efforts, such as the open sourcing of the ASP.NET framework, the company has open sourced large parts of the .NET Framework and participated in open hardware projects.

Russinovich describes the decision to make .NET open as a way of increasing interest in and usage of Microsoft's paid software. Open .NET is "an enabling technology that can get people started on other Microsoft solutions," he told the conference, continuing "It lifts them up and makes them available for our other offerings, where otherwise they might not be."

It's against that backdrop that Russinovich claimed that it was "definitely possible" that Microsoft would, one day, open source Windows, saying that "Every conversation you can imagine about what should we do with our software—open versus not-open versus services—has happened."

Releasing Windows as open source would be no small achievement. The Windows source isn't neatly packaged for easy downloading and compiling. "If you open source something but it comes with a build system that takes rocket scientists and three months to set up, what's the point?" Russinovich asked rhetorically.

Technical complexities aside, we struggle to see Microsoft releasing Windows as open source any time soon. Even as its influence wanes in the face of mobile-oriented competitors, Windows remains a huge cash cow for Redmond—one that it's unlikely to want to give up. But that doesn't mean that the company has no further open source ambitions. We could well believe that a piecemeal opening of certain parts of the Windows platform will occur over the next few years.